Just upgraded tot 0.9.16 (32-bits) and after sending some books to my e-reader (PRS-T1) I switched to another library. The following error did occur. All libraries checked out fine, though. No clue what caused this. No further problems noticed yet.

Although mentioned in the change list, I did not noticed any sync improvement/degradation either.

Edit:
This error is repeatable on every new connection to e-reader and selecting for the first time any library.

Edit 2: Version 0.9.16 is definitive causing problems with e-reader. I did a downgrade to 0.9.15 and everything is working again.